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    R Factor for Liver Injury

    Differentiates cholestatic from hepatocellular liver injury, recommended by ACG guidelines.

    INSTRUCTIONS

    Use the first lab values (ALT and ALP) indicating acute liver injury to calculate the R factor.

    When to Use
    Pearls/Pitfalls
    Why Use

    Patients with suspected drug induced liver injury (DILI) with abnormal liver chemistries.

    • The pattern of acute liver injury (and therefore the R Factor) can vary throughout the clinical course of the illness.
    • Identifying the pattern of liver injury can guide diagnostic approach to DILI, including appropriate further diagnostic testing necessary to rule out other causes of liver injury.
    • Calculating the R Factor is the first step in calculating the Roussel Uclaf Causality Assessment Method (RUCAM) when determining if liver injury is related to a specific drug.
    • Because the pattern of liver injury can evolve over time, the time point at which liver chemistries are used to calculate the R Factor can alter the final result. It is recommended that the initial liver chemistries suggesting liver injury be used, but ultimately left to the clinician to decide what set of liver chemistries to use when making an assessment.
    • The use of upper limit of normal (ULN) in the equation creates some room for variability. The ULN varies among different laboratories. This calculator uses 40 as the ULN of ALT and 120 as the ULN of ALP.
    • While not validated, the R Factor is widely used and has been incorporated into guideline recommendations for assessing liver injury.
    • Allows clinicians to collectively identify and describe the pattern of liver injury in an objective manner.
    • Allows clinicians suspecting a diagnosis of DILI to formulate an organized diagnostic strategy to rule out other causes of acute liver injury and to narrow the list of possible culprit drugs based on the pattern of liver injury.
    • Recommended by ACG guidelines.
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    Next Steps
    Evidence
    Creator Insights
    Dr. Christian Bénichou

    About the Creator

    Christian Bénichou, MD, (d. 1999) was a rheumatologist and advocate for drug safety. He served as the head of drug safety at Roussel Uclaf in France, expert reviewer for the World Health Organization's Uppsala Monitoring Centre, and on all drug safety working groups for the Council for International Organizations of Medical Sciences (CIOMS). Dr. Bénichou’s research interests were primarily monitoring of drug safety.

    To view Dr. Christian Bénichou's publications, visit PubMed

    Content Contributors
    • Zaid Tafesh, MD
    About the Creator
    Dr. Christian Bénichou
    Content Contributors
    • Zaid Tafesh, MD